I would need to compare the data sheets, but HP5 might have a straighter curve and less contrast than Tmax 100? I get really good push process results with Tmax 400, no increase in time to 800, at 1600 more like a +1 or 1.5 push then 2. I have experimented with Tmax 100 and a push, there is noticeable loss of shadow details at +1 and +2 no shadow details to speak of. That's why I would use a speed enhanced developer, Aucfine would be my choice only because I have experience with it. Tmax 100 has such fine grain that I don't grain will be noticeable in Acufine, or another such as Tmax developer, DDX, or Rodinal for that matter.